NEW YORK (Reuters Health) - Hyperactive behavior and difficulty in school share the same genetic roots, conclude the authors of a new study of twins.

The findings call into question the assumption that hyperactive kids do poorly in school due to lack of effort, as well as the idea that hyperactivity arises from frustration with difficulties in school, Dr. Kimberly J. Saudino of Boston University told Reuters Health.

"It's not just a matter of not trying hard enough," Saudino said in an interview. "These things are linked, they're genetically linked, and it's not simply a matter of effort."

The link between hyperactivity and poor academic achievement is well documented, but little understood, she and her colleague Dr. Robert Plomin of the Institute of Psychiatry in London note in the journal Child Development.

To understand if the two traits might be genetically linked, the researchers looked at 1,876 twin pairs, interviewing their parents and teachers about their behavior and comparing it to achievement as assessed by teachers. The students' average age was 7.

Scientists use twin studies to investigate whether certain traits are related to genes or the environment. Identical twin pairs share 100% of their genes, while fraternal twins share just 50%, but any set of twins raised together is theoretically exposed to an identical environment.

Plomin and Saudino found a significant genetic overlap between both hyperactive behaviors such as inattention, fidgeting, restlessness and distractibility and low academic achievement, which remained after the researchers adjusted for children's intelligence. "Our results suggest that probably somewhere around 50% of the genes that influence hyperactivity also influence academic achievement," Saudino said.

There are two possible explanations for the findings, according to the researchers. For one, some of the same genes that produce hyperactive behavior may also influence academic achievement. But it's also possible, they add, that hyperactive behavior makes it more difficult for children to learn in school -- and harder for teachers to teach them.

Given that children who were hyperactive at school behaved similarly at home, Saudino and Plomin note, it's unlikely that their behavior is a result of being frustrated in the classroom, as other researchers have suggested.

SOURCE: Child Development, May/June 2007.

REUTERS